The present invention is directed to a hydraulic power and control system and pertains more particularly to a control system for a hydraulic excavator.
Hydraulically operated material handling machines such as backhoes and hydraulic excavators have been known for some time. Such machines are extremely versatile and hence widely used in building and construction industries.
These machines normally utilize an internal combustion engine to drive one or more pumps which supply pressurized fluid to operate separate hydraulic motors for propelling the machine as well as operating the material handling implements. Considerable room exists for improvement in the efficiency and safety of existing prior art machines.
The prior art is exemplified by such U.S. Pat. Nos. as 3,428,647 issued Nov. 18, 1969 to Gerber et al; 3,476,274 issued Nov. 4, 1969 to W. J. Witwer; 3,208,221 issued Sept. 28, 1965 to J. R. Schuetz; 3,172,552 issued Mar. 9, 1965 to R. Metailler; and 2,768,499 issued Oct. 30, 1956 to J. S. Pilch.
The problem of efficiency with such machines is the result of the constant shifting between the implement motors, the need for simultaneous positive operation of a number of motors, and the need for repetitive high speed operation of a single motor. Such requirements impose unusual requirements on the construction of valves and circuits.
In order to obtain positive displacement of a motor, it must have a fluid supply unaffected by the operation of another motor. This, ideally, means a separate pump for each motor. Such an arrangement, however, could be extremely expensive and would result in a substantial waste of pump capacity during times when some of the motors are not being used. This type arrangement having separate pumps is disclosed in U.S. Pat. No. 3,172,552 issued Mar. 9, 1965 to R. Metailler.
In order to make maximum use of pump capacity, it is desirable to combine pump flow to motors which can use the increased capacity, while other motors are idle. In addition to making maximum utilization of the pump capacity, this type arrangement results in faster operation of certain machine functions. Such arrangements not only increase the efficient use of the pump capacities, but also speeds operation of the particular machine function and thereby increases the efficiency of overall material handling operation.
One proposal to increase use of pump flow is to connect the distributor valves in parallel. This arrangement, however, has the disadvantage of lack of positive control when two motors requiring different pressures are simultaneously operated. If, for example, one motor meets increased resistance, it will slow down or stop, while the other motor will speed up. Such a parallel arrangement is disclosed in U.S. Pat. No. 3,208,221 issued Sept. 28, 1965 to J. R. Schuetz.
Other proposals have included series connected distributors with the pumps combined upstream of a series of distributors. This arrangement permits use of combined flow at a particular motor but cuts off flow to downstream motors.
Still another proposal provides separate pumps and distributors with means to divert flow from one pump to combine with the flow from another for operation of one or more motors. Such an arrangement leaves a portion of the hydraulic circuit inoperative, and adds another control lever which the operator must consciously manipulate in order to use the maximum power and speed of the machine.